1. Field
This invention pertains to the field of optical measurements, and more particularly, to a system and method of measuring the curvature of an optical surface.
2. Description
While the prior art contains many theoretical and practical methods of identification of the optical power of a lens, most of them evaluate the lens' ability to bend light, and rely on the resolution of the receiving device. One of the most common methods used in lens meters uses image dimensional changes to estimate lens magnification and thus derive its optical power in diopters. Other methods rely on mechanical gages (Swiss gage) and profile-meters to actually define geometrical curvature of the lens surface and compute its power.
While every method of the identifying a lens has its merit, some of the methods used today have one or more of the following disadvantages: they take a long time; they exhibit a high sensitivity to the lens' location, positioning, material properties, and coating; and they cannot be easily automated.
Limitations to the uniformity of the refractive index of the material, and the lens thickness in combination with possible coating variations, can present significant challenges to the data fidelity of any direct imaging method of characterizing a lens. Here, a direct imaging method can be defined as one where the image produced by the lens under test is analyzed to determine the lens power.
Meanwhile, currently there is a trend toward the high scale production of semi-finished coated lenses in the spectacle lenses industry. With some lenses, the manufacturer only controls the curvature of one surface of the lens, and the lens is finished by a retailer to meet a particular customer's requirement. These lenses ate produced from variety of the materials (mostly plastics) with an even wider variety of coatings.
Therefore, since the curvature of only one surface of the product needs to be controlled and measured, there is a need for the new method and system for measuring the curvature of the lens surface.
Accordingly, it would be advantageous to provide an improved system and method of measuring the curvature of a lens surface. It would also be advantageous to provide such a system and method which do not depend upon there being any control on the curvature of the opposite surface of the lens. Other and further objects and advantages will appear hereinafter.
The present invention comprises a system and method of measuring the curvature of an optical surface of an object, such as a lens.
In one aspect of the invention, a method of measuring the curvature of a surface of an object comprises: illuminating the object surface with a light pattern having a known size to produce a virtual reflected image from the optical surface; measuring a size of the virtual reflected image produced by the optical surface from the light pattern; and calculating a curvature of the optical surface from the known size of the light pattern and the size of the virtual reflected image. Beneficially, the method includes suppressing by electronic or optical means all second and higher order reflections (“ghost images”) produced by the object from affecting the measurement of the size of the virtual reflected image.
In another aspect of the invention, a system for measuring the curvature of a surface of an object comprises: an image generator adapted to illuminate the object surface with a light pattern having a known size to produce a virtual reflected image from the object surface; an image detector for detecting the virtual reflected image from the object surface; and a controller adapted to calculate a curvature of the object surface from the known size of the light pattern and a size of the virtual reflected image detected by the image detector. Beneficially, the image generator includes a light source producing ultraviolet light or other light having a wavelength or wavelengths suitable for the object material, such as wavelengths which are absorbed by the object material yet can still trigger a detection device for detecting the virtual reflected image.